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I7r>                                        IRON

oven at 70-80" to constant, weight.1 Phosphomolybcliite x 0-0164 =

2.  Determination of the Phosphorus in presence of Arsenic.

If not more, than 0-1% of arsenic is present, the methods described above
give accurate results, but with larger proportions of arsenic., the. latter
must be eliminated from the phosphorus precipitate. After the metal
lias acted on, the silica removed, etc., as before, the hydrochloric add
solution is treated in a roomy dish, gradually and with stirring, with 10-20
c.c. of pure Irydrobromie. arid" of 1) i:\<} (containing about 48% of
hytlrobronrie acid) and evaporated to dryness on a water-bath. The arsenic
is thus volatilised, probably as the tribromide, whilst all the phosphorus
remains. The residue is taken up in dilute hydrochloric acid, the solution
evaporated in a 250 e.e. beaker to a syrup, and the phosphoric acid pre-
cipitated as usual.

3.  Determination of  Phosphorus  in  presence  of Vtuuulium. -
In  presence of vanadium,  the ammonium  phosphomolybdate,  which is
then orange coloured,  is dissolved  in  dilute  ammonia   and  the solution
evaporated to ,o c.c., a tew drops o! dilute ammonia being added from time
to time.     The enoled-slighUy ammoniacal liquid is then saturated with
ammonium chloride (5(1 grams are added), care being taken  that undis-
solvecl crystals remain in the solution.    The vanadium is thus precipitated
as ammonium metavanadate which, after h- 10 hours, is filtered and washed
with ammonium chloride solution (.',50 {'.tarns per litre) until the washings
no longer give the phosphate reaction with molvbdate, the phosphate being
then precipitated in the filtrate by means of magnesia mixture.

4.  Determination of Phosphorus in presence of Tunftsten.......In

this case the phosphomolybdate precipitate is dissolved in ammonia and
the phosphate precipitated with magnesia mixture (,s>r p,  175).

5,   Deter mi nut ion of the Sulphur

Of the vatious methods proposed, the gravimetric and volumetric
methods will be given here,

I, Gravimetric Determination, (n) M. Arnold's method8; 6
grains of the sample are mixed with t gram of potassium chlorate and
treated in a porcelain dish covered with a cluck-glass with 50 c.c. of cone.
nitric acid containing in solution i c.c. of bromine, When evolution of
gas ceases, 10 c.c. of hydrochloric acid are added and the liquid evaporated
to dryness on a sand-bath and the residue heated in an oven at 105" for
5-6 hours. The residue is then taken up in ;|o e.c. <1 hydrochloric acid,
the liquid evaporated to 10 c.c., diluted with water and the solution poured
into a (Jo c,c. measuring flask, made up to volume and filtered through a
dry pleated filter.

Of the filtrate, 50 c.c. (corresponding with 5 grams of the sample) are

1 The slight reduction of the phoHphomntvbdatf olwrt \.ihlt' touml the walls of the
.crucible has scarcely any inllucwt1 on the .uvur.tcy oi the n"ult

a The freedom of th'w acid from phosphorus must b* Hsu'i'taint-d hy ii blank test.
9 .For acting on lite metal, Oampwlon'H moditifittinn is {<iUuw'tt,free from iron and is then heated in an